Mixed-mode resizing for a video transcoder

ABSTRACT

A video transcoder for converting a compressed input video bit-stream having one spatial resolution into a compressed output video bit-stream having a different spatial resolution using a plurality of resizing channels. The transcoder has a kernel that partially decodes the compressed input video bit-stream to generate partially decoded video data. The data segments corresponding to picture portions that have both intra- and inter-predicted blocks in close spatial proximity to one another are applied to a mixed-mode resizing channel that is specifically designed for processing such data segments. For each received data segment, the control logic of the channel selects, from a bank of pre-configured resizers, a resizer that is deemed to be most suitable for resizing the image portion represented by that data segment in a computationally efficient manner. The data segment is processed in the selected resizer to generate the corresponding resized-image data. The resized-image data generated by the mixed-mode resizing channel are combined with the resized data generated by other resizing channels of the transcoder and then re-encoded to generate the compressed output video bit-stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of this application is related to that of U.S. patent application Ser. No. ______, by Denis Parfenov, Pavel Aliseychik, Aleksey Letunovskiy, Alexander Markovic, Ivan Mazurenko, and Denis Parkhomenko, attorney docket reference L09-0486US1, filed on the same date as the present application, and entitled “VIDEO TRANS CODER WITH FLEXIBLE QUALITY AND COMPLEXITY MANAGEMENT,” which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to video transcoding and, more specifically but not exclusively, to management of spatial resolution in compressed video bit-streams.

2. Description of the Related Art

This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

Video transcoding is a process of converting a previously compressed video bit-stream into another compressed video bit-stream, e.g., with a different bit rate, a different frame rate, a different display format, and/or a different coding method. For example, video transcoding can be used to convert a video bit-stream encoded in one standard into a video bit-stream encoded in a different standard, with the initial and final standards selected from a set consisting of the H.26× and MPEG-z families of standards, where x=1, 3, 4 and z=1, 2, 4. Another important example of video transcoding is conversion of a compressed video bit-stream having one spatial resolution into a compressed video bit-stream having a different (typically lower) spatial resolution, without changing the standard. Other video-transcoding operations may include adding enhanced error resilience, inserting logos and watermarks, adjusting temporal resolution, etc. Video transcoding advantageously enables multimedia devices of diverse formats and capabilities to exchange video content on heterogeneous transport-network platforms, such as the Internet.

A video transcoder can be physically placed at a transmitter, a receiver, or an intermediate node in the network. In realizing a video transcoder, the computational complexity and picture quality are usually the two most-important concerns. Another important concern is the ability to provide video transcoding on the fly, e.g., with real-time speed and without video-flow interruptions. However, accommodating these and other pertinent concerns can be a significant challenge, e.g., due to relatively large and fast variability of the network-traffic load and available transmission bandwidths.

SUMMARY

Disclosed herein are various embodiments of a video transcoder for converting a compressed input video bit-stream having one spatial resolution into a compressed output video bit-stream having a different spatial resolution using a plurality of resizing channels. The transcoder has a kernel that partially decodes the compressed input video bit-stream to generate partially decoded video data. The partially decoded data segments corresponding to picture portions that have both intra- and inter-predicted blocks in close spatial proximity to one another are applied to a mixed-mode resizing channel that is specifically designed for processing such data segments. For each received data segment, the control logic of the channel selects, from a bank of pre-configured resizers, a resizer that is deemed to be most suitable for resizing the image portion represented by that data segment in a computationally efficient manner. The data segment is processed in the selected resizer to generate the corresponding resized-image data. The resized-image data generated by the mixed-mode resizing channel are combined with the resized data generated by other resizing channels of the transcoder and then re-encoded to generate the compressed output video bit-stream.

According to one embodiment, provided is a method of resizing digital video having the steps of (i) partially decoding a first compressed video bit-stream to generate a first stream of partially decoded video data; and (ii) generating, from a first data segment of the first stream of partially decoded video data, a second data segment of video data. The first data segment represents an image portion at a first spatial resolution. The second data segment represents a corresponding image portion at a different second spatial resolution. The first data segment comprises at least one intra-predicted block and at least one inter-predicted block at the first spatial resolution. The second data segment comprises either one or more intra-predicted blocks at the second spatial resolution or one or more inter-predicted blocks at the second spatial resolution, but not both.

According to another embodiment, provided is an apparatus having (i) a decoding and resizing kernel configured to partially decode a first compressed video bit-stream to generate a first stream of partially decoded video data; and (ii) a mixed-mode resizer adapted to generate, from a first data segment of the first stream of partially decoded video data, a second data segment of video data. The first data segment represents an image portion at a first spatial resolution. The second data segment represents a corresponding image portion at a different second spatial resolution. The first data segment comprises at least one intra-predicted block and at least one inter-predicted block at the first spatial resolution. The second data segment comprises either one or more intra-predicted blocks at the second spatial resolution or one or more inter-predicted blocks at the second spatial resolution, but not both.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and benefits of various embodiments of the invention will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which:

FIGS. 1A-1D depict a video transcoder according to one embodiment of the invention;

FIGS. 2A-2E show block diagrams of a video transcoder according to another embodiment of the invention;

FIG. 3 shows a block diagram of a video transcoder according to yet another embodiment of the invention; and

FIG. 4 shows a block diagram of a mixed-mode resizer that can be used in the transcoders shown in FIGS. 2-3.

DETAILED DESCRIPTION

FIGS. 1A-D illustrate a video transcoder 100 according to one embodiment of the invention. More specifically, FIG. 1A shows a block diagram of video transcoder 100. FIGS. 1B-D show representative logical switches 192, 194, and 196 that can be used in switch banks 130 and 150 of video transcoder 100. In various embodiments, video transcoder 100 can be implemented for being placed (i) at an end-terminal equipment package having a video camera, a transmitter, a receiver, and/or a video playback device or (ii) at an intermediate node in the transport network, such as a server, a gateway, or a multipoint control unit. For illustration purposes, video transcoder 100 is described below as if it were located at an intermediate node of a network. From this description, one of ordinary skill in the art will be able to make and use, without undue experimentation, an embodiment of video transcoder 100 suitable for being placed at an end-terminal equipment package.

Referring to FIG. 1A, video transcoder 100 receives an input video bit-stream 102 having a first spatial resolution from a Network Abstraction Layer (NAL), which layer provides transport services for compressed video bit-streams as known in the art. Video transcoder 100 processes input video bit-stream 102 as further described below to generate an output video bit-stream 182 having a second (different from the first) spatial resolution. Video bit-stream 182 is applied to the NAL for being transported to the intended receiver (not explicitly shown in FIG. 1A). Both input video bit-stream 102 and output video bit-stream 182 are compressed video bit-streams that comply with a specified standard, e.g., the H.264/AVC standard, more details on which can be found in ITU-T Recommendation H.264 (11/2007), which is incorporated herein by reference in its entirety.

In one embodiment, video transcoder 100 performs planar image-size transformation from an original size/resolution (e.g., Y1 by Y2 pixels) to a target size/resolution (e.g., Z1 by Z2 pixels), where Z1=k Y1, Z2=k Y2, and k is a scaling factor (SF). Typically, the scaling factor is between zero and one (0<k<1) and can be represented as a simple fraction, k=M/N, where M and N are positive integers. Depending on the particular design objectives, different sets of M and N values can be used. The use of a few, relatively small M and N values enables a significant reduction in the computational complexity, but restricts the number of available SF values. The use of many and/or relatively large M and N values supports image transformation for a greater variety of original and target display sizes at the expense of increased computational complexity.

In various embodiments of video transcoder 100, M and N can be selected to achieve an acceptable compromise between the computational complexity and image-size flexibility. To employ relatively small M and N, and yet be able to cover a satisfactory range of target display sizes and shapes, video transcoder 100 may be configured to (i) delete several peripheral rows and/or columns of pixels in the original picture and/or (ii) add several empty (e.g., black) peripheral rows and/or columns of pixels in the target picture. In one configuration, the following relationship between the original and target sizes can be implemented: Z1=M/N Y1+b1 and Z2=M/N Y2+b2, where b1 and b2 are constants that determine the numbers of empty peripheral rows and columns, respectively. For example, to convert an image that has 960×720 pixels to an image that has 352×288 pixels, video transcoder 100 can be configured to use M=1, N=3, b1=32, and b2=48. For processing color images, substantially analogous processing can be performed for each of the constituent picture components (e.g., in the YCbCr color space) using the corresponding parallel processing channels. Depending on the particular embodiment, these parallel channels may or may not have the same architecture of the decision/control logic, such as switch configurations, mode-selection controls, etc.

Video transcoder 100 can conceptually be viewed as having a decoder portion 110 and an encoder portion 180. Decoder portion 110 and encoder portion 180 overlap as indicated in FIG. 1A and, as such, may have one or more shared elements. Decoder portion 110 performs partial decompression and decoding of input video bit-stream 102 using a decoding/resizing kernel 120. The data generated by decoding/resizing kernel 120 are applied, via a data bus 122 and switch bank 130, to a plurality of processing paths 140 ₁-140 _(K), where K is a positive integer greater than one. The output data generated by processing paths 140 ₁-140 _(K) are then applied, via switch bank 150 and a data bus 152, to an encoding kernel 170 of encoder portion 180. Based on the data received through data bus 152 and a bypass signal 124 received directly from decoding/resizing kernel 120, encoding kernel 170 generates output video bit-stream 182.

Each of switch banks 130 and 150 can generally be implemented using any desirable combination of logical switches 192, 194, and 196 shown in FIGS. 1B-D, respectively. Different instances (copies) of each particular logical switch may be configured for being traversed by the corresponding signals in different directions. For example, one or more instances of logical switch 194 may be configured for being traversed from left to right in the view presented in FIG. 1C, while one or more other instances of logical switch 194 may be configured for being traversed from right to left. Similarly, one or more instances of logical switch 196 may be configured for being traversed from left to right in the view presented in FIG. 1D, while one or more other instances of logical switch 196 may be configured for being traversed from right to left.

Video transcoder 100 has a mode controller 160 that controls the states of individual logical switches 192, 194, and 196 in switch banks 130 and 150. Using one or more logical switches 192 (FIG. 1B), mode controller 160 can controllably engage or disengage the corresponding processing path 140 connected to the switch(es). Using one or more logical switches 194 (FIG. 1C), mode controller 160 can controllably change a data flow from flowing through a first processing path 140 connected to the switch(es) to flowing through a second processing path 140 connected to the switch(es). Similarly, using one or more logical switches 196 (FIG. 1D), mode controller 160 can controllably change a data flow from flowing through one processing path 140 connected to the switch(es) to flowing through another processing path 140 connected to the switch(es), wherein logical switch 196 is connected to three or more different processing paths 140.

Mode controller 160 configures individual logical switches 192, 194, and/or 196 in switch banks 130 and 150 in accordance with a selected operating mode and/or based on a received request 158 to change the amount of computational resources allocated by the host device to the process of generating output bit-stream 182 from input bit-stream 102. Different operating modes of video transcoder 100 differ from one another by the allocated amount of processing power per video frame and the peak signal-to-noise ratio (PSNR) in the resized target-resolution image. In general, any desired number of operating modes (e.g., two or more) can be realized. However, for practical reasons, the number of operating modes may be limited to fewer than ten, e.g., five operating modes numbered zero to four.

For example, Mode 0 may be designed to provide the highest PSNR at the expense of taking up a relatively large amount of computational resources, e.g., processor time and memory utilization. Mode 1 may save processor time and reduce memory (e.g., RAM) demand compared to that of Mode 0 at the expense of producing higher levels of residual errors and the corresponding lower PSNR values. Modes 2 through 4 may further decrease computational efforts and RAM requirements in a gradual manner, e.g., by disengaging an increasingly larger number of different processing paths 140 and/or processing modules. The resulting truncated processing produces commensurate reductions in the PSNR and image quality.

In one embodiment, mode controller 160 initiates mode transitions based on the total amount of available processing power and memory in the host device, e.g., an intermediate network node having video transcoder 100. The total amount of available processing power and memory in the host device may fluctuate over time, e.g., due to the demand imposed on the computational resources of the host device by other processes/tasks. If such demand is relatively low, then mode controller 160 may put video transcoder 100 in Mode 0. If such demand increases, then mode controller 160 may gradually transition video transcoder 100 from Mode 0 to one of the operating modes selected from Modes 1 through 4 to better match the available computational resources. Subsequently, if the demand on the computational resources of the host device decreases, then mode controller 160 may gradually shift the operating mode of video transcoder 100 back toward Mode 0.

Advantageously, the ability of video transcoder 100 to dynamically engage, disengage, configure, and reconfigure various processing paths 140 allows the video transcoder to change the operating modes and therefore the picture quality in output video bit-stream 182 on the fly, without interrupting the video sequence in the output video bit-stream. More specifically, while an operating mode is being changed, video transcoder 100 continues to process the incoming sequence of video frames of bit-stream 102 to produce a corresponding sequence of video frames for bit-stream 182 so that no incoming video frame is being skipped, discarded, or dropped without being resized due to the concomitant change in the configuration of processing paths 140. In addition, certain mode transitions can be implemented without changing the data flow at all. For example, attaching certain additional processing modules to one or more already active processing paths 140 can be used to increase the processing complexity and improve the picture quality without changing the overall data flow between decoding/resizing kernel 120 and encoding kernel 170. Similarly, detaching certain processing modules from one or more active processing paths 140 without fully disengaging said processing path(s) can be used to decrease the processing complexity and lower the picture quality without a change in the overall data flow. Furthermore, certain embodiments of the invention may employ reconfigurable processing modules that enable the system to change the amount of computational resources allocated to video transcoder 100 solely through internal reconfiguration of such modules, without changing the number or external logical connections of the modules in the corresponding processing paths. Such internal reconfiguration can be performed, e.g., by changing an algorithm that is being run by the processing module in question and/or by varying the algorithm's parameters.

FIGS. 2A-E illustrate a video transcoder 200 according to another embodiment of the invention. More specifically, each of FIGS. 2A-E shows a configuration of video transcoder 200 in the corresponding operating mode. The operating modes are numbered 0 through 4, with Mode 0 being the most computationally complex mode, Mode 4 being the least computationally complex mode, and Modes 1 through 3 having different intermediate levels of computational complexity. Video transcoder 200 is generally analogous to video transcoder 100 and has switch banks that are analogous to switch banks 130 and 150 (FIG. 1). However, for clarity of description, the individual logical switches and switch banks are not explicitly shown in FIGS. 2A-E.

FIG. 2A shows a block diagram of video transcoder 200 according to its full functionality in Mode 0. Each of FIGS. 2B-E shows a block diagram of video transcoder 200 according to its reduced functionality in Modes 1-4, respectively. The functional blocks and modules of video transcoder 200 corresponding to the processing paths that are disengaged in Modes 1-4 are omitted (not explicitly shown) in the corresponding figures for clarity.

Referring to FIG. 2A, a compressed video bit-stream 202 received from the NAL is applied to an entropy decoder 204. As known in the art, entropy coding maps parameter values representing motion vectors, quantized coefficients, prediction information, and block headers into actual transmittable bits so that a smaller number of bits is assigned to more-frequently used values and a greater number of bits is assigned to less-frequently used values. Representative types of entropy coding are Variable Length Coding (VLC) and Context Adaptive Binary Arithmetic Coding (CABAC). The H.264/AVC standard also supports Context Adaptive Variable Length Coding (CAVLC). In various embodiments, entropy decoder 204 can operate based on these and other suitable types of entropy coding.

The output of entropy decoder 204 is applied to a sorting and reordering module (reorderer) 206. Reorderer 206 reorders the data received from entropy decoder 204 to put them in appropriate time sequence and sorts various data items by their type. The data need to be reordered in reorderer 206, e.g., because certain video frames may be coded, transmitted, and/or received out of their natural time sequence. Representative data-item types to be sorted may include but are not limited to (i) reference blocks, (ii) intra-prediction modes, (iii) blocks with residuals, (iv) quantization information corresponding to the blocks listed in (iii); (v) motion vectors (MVs), and (vi) reference-block dismissal information. Reorderer 206 outputs each data type on a corresponding output line of data busses 208 a-b. For example, reorderer 206 directs quantized data items to an inverse quantizer (Q⁻¹) 210, where said data items are subjected to inverse quantization as known in the art.

Reorderer 206 and inverse quantizer 210 feed three parallel resizing channels: an intra-mode resizing channel, a mixed-mode resizing channel, and an inter-mode resizing channel. These three resizing channels are used for generating target-resolution blocks from original-resolution blocks while taking into account the types of prediction employed in the corresponding original-resolution frames. More specifically, the intra-mode resizing channel, which is represented by an intra-cache memory 214 and an intra resizer 220, deals with intra-predicted blocks. As known in the art, intra prediction is a process of predicting pixels in a block based on previously coded data corresponding to the neighboring blocks from the same video frame. The inter-mode resizing channel, which is represented by an inter-cache memory 216, an inter resizer 228, and an MV-primary resizer 232, deals with inter-predicted blocks. As known in the art, inter prediction is a process of predicting pixels in a current frame from similar regions in one or more previously coded frames.

The mixed-mode resizing channel, which is represented by a mixed-mode resizer 224, deals with instances of frames for which a target-resolution block corresponds to a portion of the original-resolution image that has both an inter-predicted block and an intra-predicted block. A demultiplexer switch 212 is used to de-multiplex the various data blocks or data segments that appear at the output of inverse quantizer 210 and direct them to the appropriate one of the three resizing channels. As used herein, the term “data segment” refers to a basic unit of data that can be processed, alone or in combination with one or more other “data segments” by the intended receiving processing module, channel, or path. In various embodiments, the data segments directed by demultiplexer switch 212 to the intra-mode resizing channel, the mixed-mode resizing channel, and the inter-mode resizing channel may or may not have the same structure. Note that all three resizing channels are used in each of Modes 0 through 4 (see FIGS. 2A-2E, respectively), even though the channel-implementation complexity may depend on the particular operating mode. Advantageously, the intra-mode resizing channel, the mixed-mode resizing channel, and the inter-mode resizing channel can operate in parallel on the respective streams of demultiplexed data, thereby reducing the processing delay and the lag between compressed input video bit-stream 202 and a compressed output video bit-stream 298.

In one embodiment, the intra-mode resizing channel, the mixed-mode resizing channel, and the inter-mode resizing channel operate in the transform domain. For this embodiment, a DCT (discrete cosine transform; labeled T in FIG. 2) module 270, located in the encoder portion of transcoder 200 and shown using a dashed line, is omitted. In an alternative embodiment, the intra-mode resizing channel, the mixed-mode resizing channel, and the inter-mode resizing channel operate in the spatial domain. For this embodiment, DCT module 270 is not omitted, and each of the three resizing channels incorporates or is preceded by an inverse DCT module (not explicitly shown in FIG. 2).

In the description that follows, the inter-mode resizing channel is described first, the intra-mode resizing channel is described second, and the mixed-mode resizing channel is described third. In the encoder portion of transcoder 200, which is located in the view of FIG. 2A to the right of a deblocking filter 240 and a decoder-history buffer 244 d, the processing corresponding to the intra-mode, mixed-mode, and inter-mode resizing channels becomes convoluted. For example, the mixed-mode resizing channel terminates in the decoder portion of transcoder 200 while feeding its processing results into the extensions of inter- and intra-mode resizing channels. Due to these and other pertinent design features of transcoder 200, the description below of one resizing channel may refer to certain elements of another resizing channel. This cross-referencing of the resizing channels in the description should not be construed to improperly attribute circuit elements corresponding to the convoluted portions and extensions of the resizing channels exclusively to one or the other resizing channel.

Mixed-mode resizer 224, inter resizer 228, and MV-primary resizer 232 are configured to receive MV data directly from reorderer 206, via bus 208 a. Based on the received MV data, MV-primary resizer 232 searches for a best fit to the MV-data aggregate at the target resolution. The MV-data aggregate represents the dominating motion among the corresponding (e.g., 4×4) blocks to be fused in the resizing operation, and the best fit is an MV corresponding to that dominant motion. While generating said best fit, MV-primary resizer 232 takes into account relative temporal lags and scales the resulting dominant MV using an appropriate scaling factor (SF, k). The scaled dominant MV is fed to a resized-MC module 236 and an ME engine 256, with MC and ME standing for motion compensation and motion estimation, respectively. As known in the art, motion compensation comprises a step of subtracting an inter-predicted block from the corresponding reference block to generate residuals. Motion estimation comprises a step of finding a suitable inter prediction, e.g., a reference block and a corresponding motion vector. Both resized-MC module 236 and ME engine 256 use the scaled dominant MV received from MV-primary resizer 232 as an initial guess for further MV search and refinement, e.g., based on residual-error minimization. The use of the scaled dominant MV in resized-MC module 236 and ME engine 256 advantageously makes the search and refinement performed thereafter less computationally intense and more efficient.

ME engine 256 also receives (i) target-resolution blocks corresponding to formerly intra-predicted blocks from deblocking filter 240, (ii) reference blocks from an encoder-history buffer 244 e, and (iii) a feedback signal 254 generated by a feedback loop comprising an MC module 258, an adder 266, optional DCT module 270, a quantizer (Q) 274, an inverse quantizer (Q⁻¹) 278, an IDCT (inverse DCT; labeled T⁻¹ in FIG. 2A) module 282, an adder 262, and a deblocking filter 242. ME engine 256 uses these inputs in general and feedback signal 254 in particular to (i) iteratively find optimal MVs that minimize the residual energy and temporal drift for series of inter-coded target-resolution blocks and (ii) decrease visual artifacts caused, e.g., by (a) the process of fusing two or more blocks of original resolution into a single block of target resolution and (b) the inherent precision loss due to the quantization and the DCT transform. The feedback loop implements a so-called “reconstruction path,” which serves, e.g., to minimize the residual errors and reduce blocking distortions and distortions associated with DCT and quantization. For example, deblocking filter 242 filters the blocks received from adder 262 before storing them as reference blocks in encoder history buffer 244 e for MV refinement and future predictions to achieve at least the following two benefits: (1) block edges are smoothed, thereby improving the appearance of decoded images, particularly at higher compression ratios, and (2) the filtered blocks can be used for motion compensation in further frames, which results in a smaller residual error after the inter prediction. Note that the feedback-loop processing may include two or more feedback-loop cycles, with the results of this feedback-loop processing being stored/updated in encoder-history buffer 244 e after each of the feedback-loop cycles.

Inter resizer 228 receives inter-predicted blocks from inverse quantizer 210 via demultiplexer switch 212 and inter-cache memory 216. Recall also that inter resizer 228 receives MV data from reorderer 206. Due to having access to multiple relevant inter-predicted blocks in inter-cache memory 216, inter resizer 228 is able to perform a residual-error joining operation for various blocks that are being fused to form the corresponding target-resolution blocks in a relatively efficient manner. More specifically, inter resizer 228 scales down (or up) the original blocks of residuals retrieved from inter-cache 216 while appropriately fusing them to obtain resized blocks of residuals for subsequent reconstruction of the corresponding image blocks in an adder 230. Adder 230 directs the reconstructed image blocks to deblocking filter 240.

Intra resizer 220 is coupled to inverse quantizer 210 in a manner similar to that of inter resizer 228. More specifically, intra resizer 220 receives intra-predicted and reference blocks from inverse quantizer 210 not directly, but via demultiplexer switch 212 and intra-cache memory 214. Demultiplexer switch 212 selects the reference blocks intended for intra prediction in the output of inverse quantizer 210 and directs them to intra-cache memory 214, where these blocks are temporarily stored for further processing in intra resizer 220. Intra resizer 220 also receives the original-resolution intra modes directly from reorderer 206 via bus 208 b. Intra resizer 220 retrieves sets of related blocks from intra-cache memory 214, optionally performs an inverse DCT operation on them, removes intra-coding from the intra-predicted blocks, and fuses the resulting original-resolution blocks to form the corresponding target-resolution blocks. These target-resolution blocks are then directed to deblocking filter 240.

An intra-mode estimator 248 receives (i) the original-resolution intra modes directly from reorderer 206 via bus 208 b, (ii) target-resolution blocks intended for intra prediction from deblocking filter 240, and (iii) a feedback signal 246 generated by a feedback loop having an intra predictor 252, adder 266, embodiment-specific DCT module 270, quantizer 274, inverse quantizer 278, and IDCT module 282. Intra-mode estimator 248 uses these inputs in general and feedback signal 246 in particular to produce a reduced set of refined intra modes at the target resolution. More specifically, feedback signal 246 is used both to decrease compression artifacts (e.g., by minimizing the residual energy) and to find more-precise intra modes. Note that the feedback loop that generates feedback signal 246 for intra-mode estimator 248 shares certain elements with the feedback loop that generates feedback signal 254. A multiplexer switch 260 is used to appropriately engage the shared elements to enable appropriate signal processing by each of these two feedback loops.

As already indicated above, an original-resolution video frame may have both intra- and inter-predicted blocks. Such frames may be routinely encountered when certain advanced video-coding techniques are used, such as some of the coding techniques specified in the H.264/AVC standard. When an inter-predicted block and an intra-predicted block are located in relatively close spatial proximity to one another in the original-resolution video frame, a resolution change effected by the transcoder may cause these blocks to have to be fused together into a single block at the target resolution. In fact, there may exist a rather large number of possible geometrical combinations of such blocks and the corresponding inter- and intra-prediction modes. For example, for k=⅓, there are more than 6·10⁸ possible geometrical combinations, which makes constructing the corresponding ad hoc mixed-mode resizers impractical. Mixed-mode resizer 224 addresses this problem in transcoder 200 as further described below.

Mixed-mode resizer 224 is designed to decode co-located intra- and inter-predicted blocks and fuse them together to form a corresponding target-resolution block. In one embodiment, the output format employed by mixed-mode resizer 224 is the same as the output format employed by inter-resizer 228 and intra resizer 220. While processing co-located intra- and inter-predicted blocks, mixed-mode resizer 224 makes a decision on whether intra coding or inter coding is more beneficial for the fused target-resolution block(s). Mixed-mode resizer 224 can make this decision, e.g., based on intra-mode residuals, the MV data, and inter-mode residuals received from intra-cache memory 214, reorderer 206, and inter-cache memory 216, respectively. For example, if the MVs corresponding to the inter-predicted blocks are approximately co-directional and the inter-predicted blocks dominate over the intra-predicted blocks, then inter-prediction coding with one or more corresponding reference blocks is chosen for the target resolution. If the inter-predicted blocks do not dominate, then intra-prediction coding may be chosen for the corresponding target-resolution block(s). A mixed-mode resizer that can be used as mixed-mode resizer 224 is described in more detail below in reference to FIG. 4.

Deblocking filter 240 receives resized blocks and other relevant data from each of the intra-mode resizing channel, the mixed-mode resizing channel, and the inter-mode resizing channel, e.g., as indicated in FIG. 2A. Deblocking filter 240 operates on the received data to (i) remove all inter- and intra-prediction coding and (ii) reduce visual artifacts originated from motion compensation and block fusing and resizing to target resolution. The processed blocks corresponding to formerly intra-predicted blocks are supplied to intra-mode estimator 248 for intra-prediction processing and data compression at the target resolution. Similarly, the processed blocks corresponding to formerly inter-predicted blocks are supplied to ME engine 256 for inter-prediction processing and data compression at the target resolution. Some or all of the processed blocks are also temporarily stored in decoder-history buffer 244 d. These stored blocks can be retrieved from decoder-history buffer 244 d by resized-MC module 236 and mixed-mode resizer 224 and used thereat as reference blocks for motion tracking.

Decoder-history buffer 244 d is partially or fully purged as appropriate or necessary to delete the blocks that are no longer useful for their intended purposes. For example, a block-dismissal command 218 generated by reorderer 206 can be used to set an expiration time for the blocks stored in both history buffers 244 d and 244 e. In a representative configuration, the expiration time for a set of blocks used for inter- and/or intra-prediction processing may correspond to the latest time at which any block in the set is expected to be retrieved from history buffers 244 d and 244 e for said processing. Block-dismissal command(s) 218 notify the buffer controller (not explicitly shown in FIG. 2) when certain reference blocks can be purged from history buffers 244, thereby enabling the history buffers to advantageously have a smaller overall size than without the use of the block-dismissal command(s).

The use of two separate history buffers, i.e., history buffers 244 d and 244 e, for the decoder and encoder portions, respectively, of transcoder 200 serves to optimize motion estimation and motion compensation for the generation of compressed output video bit-stream 298. More specifically, history buffers 244 d and 244 e receive and store data corresponding to the same blocks, with the same resolution, but with different levels of residual errors, wherein each of the levels is more beneficial for the intended data usage than the other. For example, decoder history buffer 244 d receives and stores relatively high-quality blocks that have not been subjected to distortion due to DCT and/or quantization. These blocks are used, e.g., when ME engine 256 attempts to approximate them at target resolution. Similarly, encoder-history buffer 244 e contains the current approximation of the contents of decoder-history buffer 244, wherein said approximation takes into account DCT-, quantization-, and ME-induced aberrations. An added benefit of employing the two history buffers instead of one is that the relatively large amount of data transfers to various locations within transcoder 200 is split between two different sets of memory banks, which alleviates the disadvantageously heavy data-transfer load that a single set of memory banks would otherwise encounter.

A reorderer 286 receives: (i) the optimized intra mode(s), via line 250, directly from intra-mode estimator 248, (ii) the optimized motion vector(s), via line 268, directly from ME engine 256, (iii) block dismissal commands 218, and (iv) quantized blocks of residuals from quantizer 274. The quantized blocks of residuals are generated after adder 266 generates blocks of residuals corresponding to the optimized intra mode(s) and motion vector(s) and directs these blocks to optional DCT module 270 and/or to quantizer 274. Based on the received inputs, reorderer 286 assembles a corresponding sequence of data segments for an entropy encoder 290. Entropy encoder 290 applies entropy coding to the received data segments to generate output video bit-stream 298 for the NAL.

FIG. 2B shows a block diagram of video transcoder 200 according to its reduced functionality in Mode 1. One difference between the configurations shown in FIGS. 2B and 2A is that encoder-history buffer 244 e (FIG. 2A) is now disengaged. Also, decoder-history buffer 244 d (FIG. 2A) is now connected to ME engine 256 and MC module 258 and is renamed a shared-history buffer 244 s (FIG. 2B). These configuration changes can be made on the fly, without affecting the data flow in transcoder 200 or producing any interruptions in the video sequence of output video bit-stream 298.

Encoder-history buffer 244 e can be disengaged in Mode 1 substantially without any loss of functionality because, as already indicated above, encoder-history buffer 244 e and decoder-history buffer 244 d have similar contents. Therefore, the video blocks stored in decoder-history buffer 244 d can be used as an approximation of the corresponding blocks stored in encoder-history buffer 244 e. Since this approximation is inherently different from the blocks used for the same purpose in Mode 0, a reconfiguration of transcoder 200 into Mode 1 causes a drop in video quality for output video bit-stream 298.

While transcoder 200 operates in Mode 1, both ME engine 256 and MC module 258 receive reference blocks from shared-history buffer 244 s. Motion-compensated reference blocks produced by MC module 258 undergo feedback-loop processing as already described above for Mode 0, and the processed blocks come back to ME engine 256 via feedback signal 254. As in Mode 0, feedback signal 254 enables ME engine 256 to optimize the corresponding motion vectors while taking into account MC-, DCT-, and quantization-originated errors induced in the encoder portion of transcoder 200. However, unlike in Mode 0, MC module 258 implements a motion-compensation scheme in which the blocks of residuals are computed based on reference blocks that have not been refined to take into account the quantization- and/or DCT-originated errors. The latter characteristic of Mode 1 leads to an incremental quality drop compared Mode 0, but reduces the amount of required memory almost by a factor of two because history buffers 244 d and 244 e typically have a much larger size than cache memories 214 and 216. In addition, less precise and therefore less computationally taxing motion-estimation algorithms can now be employed in ME engine 256 without a noticeable detrimental effect on the video quality provided by output video bit-stream 298.

FIG. 2C shows a block diagram of video transcoder 200 according to its reduced functionality in Mode 2. One difference between the configurations shown in FIGS. 2C and 2B is that ME engine 256 (FIG. 2B) is disengaged. The motion-compensation feedback loop is reconfigured so that (1) feedback signal 254 generated by said feedback loop is applied to MC module 258 and (2) the motion vectors produced by primary-MV resizer 232 are passed by resized MC module 236 via line 238 directly to reorderer 286. Since the motion vectors produced by primary-MV resizer 232 are less accurate than the motion vectors produced by ME engine 256, the blocks of residuals directed by adder 266 toward reorderer 286 have a greater residual energy than in Mode 1, which results in a concomitant quality drop for output video bit-stream 298.

As an additional means of reducing the computational complexity in Mode 2, deblocking filter 242 may be optionally disengaged. The optional nature of this disengagement is indicated in FIG. 2C by the dashed line that shows the outline of deblocking filter 242. Although the disengagement of deblocking filter 242 can lead to certain visual artifacts in output video bit-stream 298, the additional video-quality drop corresponding to these artifacts is not very significant and the resulting video quality may still be considered to remain within the general bounds of the video quality designated for Mode 2.

FIG. 2D shows a block diagram of video transcoder 200 according to its reduced functionality in Mode 3. One significant difference between the configurations shown in FIGS. 2D and 2C is that the motion-compensation feedback loop is now disengaged, thereby producing an open-MC-loop configuration. More specifically, MC module 258 is bypassed and excluded from the path between deblocking filter 240 and multiplexer 260. As a result, no DCT- and/or quantization-induced error compensation is performed for inter-predicted blocks in the encoder portion of transcoder 200. Similar to other open-loop architectures, the opening of the MC-feedback loop in Mode 3 of transcoder 200 may cause some temporal drift in the video provided by output video bit-stream 298.

Another difference is that shared history buffer 244 s is disengaged. This disengagement causes mixed-mode resizer 224 to perform a simplified version of mixed-mode resizing processing with less precise or completely disabled motion compensation. Resized-MC module 236 and adder 230 are disengaged. Adder 266 is bypassed, and adder 262 is reconfigured from performing a “sum” operation to performing a “subtraction” operation. As a result, in Mode 3, deblocking filter 240 receives and processes blocks of residuals directly from inter resizer 228, as opposed to receiving reconstructed inter-predicted target-resolution blocks from adder 230 in Mode 2.

FIG. 2E shows a block diagram of video transcoder 200 according to its reduced functionality in Mode 4. One significant difference between the configurations shown in FIGS. 2E and 2D is that the intra-prediction feedback loop (see, e.g., feedback signal 246 in FIG. 2D) is disengaged. This disengagement is achieved by disconnecting adder 262, IDCT module 282, and inverse quantizer 278. Also, an intra-coder module 253 replaces, in the configuration of FIG. 2E, the intra-predictor module 252 of FIG. 2D. Intra-coder module 253 does not need or use a feedback signal from an intra-prediction feedback loop and, as such, implements a simpler version of intra-prediction coding. Intra-mode estimator 248 is also reconfigured to operate based solely on the inputs received from the decoder portion of transcoder 200 and without feedback signal 246.

As an additional means of reducing the computational complexity in Mode 4, deblocking filter 240 may be optionally disengaged and replaced by an interconnect switch (not explicitly shown). A main function of the interconnect switch is to properly route the resized blocks generated by mixed-mode resizer 224 to either the intra-prediction path or the inter-prediction path, which paths are labeled “intra path” and “inter path,” respectively, in FIG. 2E. The optional nature of the disengagement of deblocking filter 240 is indicated in FIG. 2E by the dashed line that shows the outline of the deblocking filter.

FIG. 3 shows a block diagram of a video transcoder 300 according to yet another embodiment of the invention. Transcoder 300 is generally analogous to transcoder 200 (FIG. 2) and uses many of the same circuit elements and modules. The labeling for these circuit elements/modules is unchanged from FIG. 2. However, unlike FIG. 2, FIG. 3 explicitly shows various logical switches that enable transitions between different operating modes for transcoder 300. Similar to transcoder 200, transcoder 300 supports five operating modes numbered 0 through 4. In FIG. 3, logical-switch terminals have labels that indicate the operating-mode number(s) corresponding to each terminal For example, label “234” means that the corresponding switch terminal is used during each of Mode 2, Mode 3, and Mode 4. As another example, label “01” means that the corresponding switch terminal is used during Modes 0 and 1. As yet another example, label “2” means that the corresponding switch terminal is only used during Mode 2.

A compressed video bit-stream 302 received from the NAL is applied to a decoding/resizing kernel 310. In one embodiment, decoding/resizing kernel 310 comprises: (i) entropy decoder 204; (ii) reorderer 206; (iii) inverse quantizer 210; (iv) demultiplexer switch 212; (v) intra-cache memory 214; (vi) intra resizer 220; (vii) mixed-mode resizer 224; (viii) inter-cache memory 216; (ix) inter resizer 228, and (x) MV-primary resizer 232, all interconnected as shown, e.g., in FIG. 2A. Lines 312 and 314 couple intra resizer 220 and mixed-mode resizer 224, respectively, to deblocking filter 240. Logical switches 316 a-b are used to engage or disengage adder 230. Logical switches 318 a-b are similarly used to engage or disengage resized-MC module 236. More specifically, both adder 230 and resized-MC module 236 are engaged in Modes 0 through 2 and bypassed in Modes 3 and 4.

Transcoder 300 has a buffer controller 320 that controls history buffers 244 d and 244 e. Buffer controller 320 supports the functions of a conventional memory controller and executes them as appropriate upon certain mode transitions. For example, buffer controller 320 may send (i) an “initialize buffer” command to decoder history buffer 244 d upon a transition from any of Modes 3-4 to any of Modes 0-2 or during a system boot-up into any of Modes 0-2; (ii) a “purge buffer” command to decoder history buffer 244 d upon a transition from any of Modes 0-2 to any of Modes 3-4; (iii) a “purge buffer” command to encoder history buffer 244 e upon a transition from Mode 0 to any of Modes 1-4; and (iv) a “dismiss frame/block” command to either of the history buffers. The latter command is usually sent out based on frame/block dismissal instructions 218 received from decoding/resizing kernel 310. Buffer controller 320 may also configure either of history buffers 244 d and 244 e to provide a copy of its contents, via a logical switch 328, to the other history buffer. Logical switches 324 and 326 are used to connect decoder history buffer 244 d to decoding/resizing kernel 310 and deblocking filter 240, respectively. Both of logical switches 324 and 326 are closed (conducting) in Modes 0-2 and open (non-conducting) in Modes 3 and 4. Logical switches 344 and 346 connect history buffers 244 d and 244 e to ME engine 256. More specifically, logical switch 344 connects (i) encoder history buffer 244 e to line 345 in Mode 0 and (ii) decoder history buffer 244 d to line 345 in Modes 1 and 2. Logical switch 344 is open in Modes 3 and 4. Logical switch 344 is closed in Modes 0 and 1 and open in Modes 2-4.

Logical switches 332, 334 a, and 336 are used to manage the external connections of deblocking filter 242. More specifically, logical switch 332 connects deblocking filter 242 to encoder history buffer 244 e in Mode 0 and is open in Modes 1-4. Logical switch 334 a connects deblocking filter 242 to (i) ME engine 256 in Modes 0 and 1 and (ii) MC module 258 in Mode 2. Logical switch 334 a is open in Modes 3 and 4. Logical switch 334 b operates synchronously with logical switch 334 a as indicated in FIG. 3. Logical switch 334 b connects line 333 to (i) ME engine 256 in Modes 0 and 1 and (ii) line 335 in Mode 2. Logical switch 334 b is open in Modes 3 and 4. Logical switch 336 connects deblocking filter 242 to line 337 in Modes 0-2 and is open in Modes 3 and 4.

Logical switches 330, 348 a-b, and 350 are used to manage data routing from deblocking filter 240, through or around one or both of ME engine 256 and MC module 258, to multiplexer switch 260. In Modes 3 and 4, logical switches 330 and 350 are configured so that both ME engine 256 and MC module 258 are bypassed. In Mode 2, logical switches 330, 348 a-b, and 350 are configured so that only ME engine 256 is bypassed. In Modes 0 and 1, logical switches 330, 348 a-b, and 350 are configured to engage both ME engine 256 and MC module 258 in the data processing.

Logical switch 356 is used to connect reorderer 286 to an appropriate source of motion vectors. More specifically, in Modes 0 and 1, logical switch 356 configures reorderer 286 to receive motion vectors from ME engine 256. In Mode 2, logical switches 356, 334 b, and 318 b configure reorderer 286 to receive motion vectors from resized-MC module 236. In Modes 3 and 4, logical switches 356 and 318 a configure reorderer 286 to receive motion vectors from decoding/resizing kernel 310.

Logical switches 338, 352, 362 a-b, 366 a-b, and 368 are used to manage the two feedback loops, i.e., the reconstruction-path feedback loop and the intra-prediction feedback loop. The description of these feedback loops provided above in reference to FIGS. 2A-2E similarly applies to FIG. 3. Each of logical switches 338, 352, and 368 is closed in Modes 0-3 and open in Mode 4. Logical switches 362 a-b are used to engage or disengage a sign inverter 364. More specifically, logical switches 362 a-b are configured to (i) exclude sign inverter 364 from the processing path between IDCT module 282 and adder 262 in Modes 0-2 and (ii) include sign inverter 364 in that processing path in Modes 3-4. When sign inverter 364 is engaged, adder 262 in effect operates as a subtractor because the sign inverter changes the sign of one of the adder's inputs. Logical switches 366 a-b are used to engage or disengage adder 266. More specifically, logical switches 366 a-b are configured to (i) exclude adder 266 from the processing path between multiplexer switch 260 and DCT module 270 in Modes 3 and 4 and (ii) include adder 266 in that processing path in Modes 0-2.

FIG. 4 shows a block diagram of a mixed-mode resizer 400 that can be used as mixed-mode resizer 224 in transcoder 200 (FIG. 2) or transcoder 300 (e.g., as a part of decoding and resizing kernel 310, FIG. 3) according to one embodiment of the invention. Mixed-mode resizer 400 is illustratively shown as being coupled to reorderer 206, intra-cache memory 214, inter-cache memory 216, decoder/shared history buffer 244, and deblocking filter 240 of transcoder 200 (FIG. 2). However, based on the description that follows, one of ordinary skill in the art will be able to configure mixed-mode resizer 400 for use in transcoder architectures that are different from the architecture of transcoder 200.

Mixed-mode resizer 400 receives, via line 404, the original-resolution blocks that are to be fused together to form a corresponding target-resolution block. For various original-resolution blocks, the coding type is also indicated, which can be, e.g., “skip” (i.e., no intra- or inter-prediction coding), “intra coded,” “inter coded,” etc. Mixed-mode resizer 400 also receives the original-resolution intra modes and motion vectors via lines 406 and 408, respectively. Lines 404-408 are coupled to a coding-decision module 402 designed to determine the coding type for each prospective target-resolution block based on the analysis of received data. The coding type for target resolution blocks can similarly be “skip,” “intra coded,” “inter coded,” etc.

In one embodiment, coding-decision module 402 applies the following exemplary set of rules to analyze the data that appear on lines 404-408:

-   -   (A) if all relevant original-resolution blocks have the “skip”         coding type, then the coding type for the corresponding         target-resolution block is set to “skip”;     -   (B) if R>Ro, then the coding type for the target-resolution         block is set to “intra coding,” where R₀ is a positive constant         smaller than one; parameter R is defined as         R=(N_(intra)+1)/(N_(inter)+1); N_(intra) is the number of         intra-predicted original-resolution blocks; and N_(inter) is the         number of inter-predicted original-resolution blocks;     -   (C) if all motion vectors of the relevant inter-predicted         original-resolution blocks point to neighboring blocks, then the         coding type for the target-resolution block is set to “inter         coding;”     -   (D) if all motion vectors corresponding to inter-predicted         original-resolution blocks are oriented within an angular sector         having a selected, relatively narrow angular width, then the         coding type for the corresponding target-resolution block is set         to “inter coding;”     -   (E) if none of rules (A)-(D) is satisfied, then the coding type         for the target-resolution block is set to “intra coding.”         Rules (A)-(E) are hierarchical and have a decreasing priority         going from rule (A) to rule (E), meaning that any particular         rule is used for making the coding decision only if all         higher-priority rules are not applicable to the set of         original-resolution blocks in question. In alternative         embodiments, other rule sets can similarly be used in         coding-decision module 402.

If coding-decision module 402 determines that the coding type for the target-resolution block is going to be “intra coding,” then the coding-decision module sends an enable signal 418 to an intra-mode selector 420. Alternatively, if coding-decision module 402 determines that the coding type for the target-resolution block is going to be “inter coding,” then the coding-decision module sends an enable signal 428 to an inter-mode selector 430.

Intra-mode selector 420 analyzes the original-resolution blocks and the original-resolution intra modes received via lines 404 and 406, respectively, and predicts an intra mode that is most likely to be used for encoding the corresponding target-resolution block in the encoder portion of the transcoder. The predicted intra mode is communicated, via line 422, to a switch controller 440. In one embodiment, the predicted intra mode can also be used as an initial intra-mode approximation in the intra-prediction feedback loop (see, e.g., feedback signal 246 in FIG. 2A).

Inter-mode selector 430 analyzes the original-resolution blocks and the original-resolution motion vectors received via lines 404 and 408, respectively, and selects a reference block for inter-prediction coding based on said analysis. Inter-mode selector 430 then computes an estimated motion vector corresponding to the selected reference block. The selected reference block and the computed motion vector are communicated, via lines 432 and 434, respectively, to switch controller 440.

Switch controller 440 uses the data received via lines 422, 432, and 434 to select a suitable resizer 452 _(i) from a bank 450 of resizers 452 ₁-452 _(P). The selection can be based, e.g., on (i) the type of coding selected for the target-resolution block by coding-decision module 402, (ii) relative geometric positions in the original-resolution frame of the inter- and intra-predicted blocks that are to be fused together to form a corresponding target-resolution block, (iii) the predicted intra mode, and (iv) the estimated motion vector(s). Switch controller 440 then configures switches 448 and 454 to direct the mixed-mode resizing processing through the selected resizer 452 _(i). The output of the selected resizer 452 _(i) becomes the output of mixed-mode resizer 400.

Bank 450 has P different resizers 452, where P is a positive integer greater than one. Each individual resizer 452 is designed and configured to handle the corresponding specified range(s), set(s), and/or ensemble(s) of (i) relative inter-predicted and intra-predicted block positions within the frame, (ii) intra modes, and/or (iii) motion vectors. After being selected by switch controller 440, resizer 452 _(i) receives the above-described data transmitted via lines 404-408. In addition, resizer 452 _(i) receives (i) reference blocks and blocks of residuals for intra-prediction coding, e.g., from intra-cache memory 214, (ii) blocks of residuals for inter-prediction coding, e.g., from inter-cache memory 216, and/or (iii) reference blocks for motion compensation, e.g., from history buffer 244. Note that the reference blocks and blocks of residuals for intra-prediction coding and the blocks of residuals for inter-prediction coding have the original resolution while the reference blocks for motion compensation have the target resolution. Using the received data, resizer 452 _(i) performs a corresponding resizing operation to generate a resized block for transfer, e.g., to deblocking filter 240. Depending on the particular embodiment of the transcoder in which mixed-mode resizer 400 is deployed, individual resizers 452 can be designed to operate in the spatial domain or in the transform domain.

As used herein, the term “processing path” refers to one or more processing modules, blocks, and/or elements of a transcoder that are (i) operatively connected to one another, if there are more than one of them, and (ii) coupled between at least two logical switches, wherein each of said at least two logical switches may be one of logical switches 192, 194, and/or 196. Multiple explicit examples of “processing paths” can be found, e.g., in FIG. 3. A first representative example of a “processing path” shown in FIG. 3 comprises resized-MC module 236, which is coupled between logical switch 318 a and logical switch 318 b. A second representative example of a “processing path” shown in FIG. 3 comprises inverse quantizer 278 and IDCT module 282, which are coupled between logical switch 368 and logical switch 362 b. A third representative example of a “processing path” shown in FIG. 3 comprises history buffer 244 d, history buffer 244 e, and MC module 258, which are coupled between logical switch 324 and logical switch 350. One skilled in the art will be able to find several additional examples of processing paths in FIG. 3.

As used herein, the term “block” refers to an image-compression component used in video compression. A block (also often referred to in the literature as “macroblock”) comprises two or more pixels. More specifically, the particular size of a block depends on the codec and is usually a multiple of four pixels. The most frequently used block sizes are 4×4, 8×8, and 16×16 pixels. A block may also have a rectangular shape, with the height being 4, 8, 12, or 16 pixels and the width being 4, 8, 12, or 16 pixels, wherein the height is different from the width. For the purposes of this specification, the terms “block” and “macroblock” should be regarded as interchangeable.

Color information may be encoded at a lower resolution than the luminance information. For example, the color information of an 8×8 block in a 4:1:1 color space is encoded using a YCbCr format, wherein the luminance is encoded in an 8×8 pixel format while the difference-red and difference-blue information is encoded in a 2×2 pixel format.

As known in the art, the term “spatial resolution” generally refers to the amount of detail that an image holds. Higher spatial resolution typically corresponds to more image detail. Image resolution can be measured in various ways. For example, image resolution can be used to quantify how close two lines can be to each other to still be perceived as separate lines in the image. Resolution units can be tied to physical sizes (e.g., lines per inch), to the overall size of a picture (e.g., lines or pixels per height/width of the picture), or to angular subtenant. Line pairs are often used instead of lines, with a line pair comprising a dark line and an adjacent light line. In television, a resolution of ten lines per millimeter means five dark lines alternating with five light lines per millimeter. In digital imaging, resolution is usually tied to the pixel count in an image. More specifically, it is often said that an image has a vertical resolution of N pixels and a horizontal resolution of M pixels, e.g., 640×480 pixels. Another popular convention is to cite resolution as the total number of pixels in the image, which is calculated by multiplying the number of pixel columns by the number of pixel rows. Other conventions include describing resolution in pixels per length unit or pixels per area unit, such as pixels per inch or pixels per square inch.

In various embodiments, an “integer transform” can be employed, as known in the art, instead of or in addition to the DCT transform, e.g., in modules 270 and 282. A transcoder of the invention can have fewer or more than five operating modes.

The present inventions may be embodied in other specific apparatus and/or methods. The described embodiments are to be considered in all respects as only illustrative and not restrictive. In particular, the scope of the invention is indicated by the appended claims rather than by the description and figures herein. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range.

It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims.

The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures.

Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

Also for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements.

The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they formally fall within the scope of the claims.

A person of ordinary skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers/processors. Herein, some embodiments are intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions where said instructions perform some or all of the steps of methods described herein. The program storage devices may be, e.g., digital memories, magnetic storage media, such as magnetic disks or tapes, hard drives, or optically readable digital data storage media.

The functions of the various elements shown in the figures, including any functional blocks labeled as “processors,” may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non volatile storage. Other hardware, conventional and/or custom, may also be included. Similarly, any switches shown in the figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the implementer as more specifically understood from the context.

It should be appreciated by those of ordinary skill in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 

What is claimed is:
 1. A method of resizing digital video, the method comprising: partially decoding a first compressed video bit-stream to generate a first stream of partially decoded video data; and generating, from a first data segment of the first stream of partially decoded video data, a second data segment of video data, wherein: the first data segment represents an image portion at a first spatial resolution; the second data segment represents a corresponding image portion at a second spatial resolution, the second spatial resolution being different from the first spatial resolution; the first data segment comprises at least one intra-predicted block and at least one inter-predicted block at the first spatial resolution; and the second data segment comprises either one or more intra-predicted blocks at the second spatial resolution or one or more inter-predicted blocks at the second spatial resolution, but not both.
 2. The method of claim 1, further comprising demultiplexing the partially decoded video data to generate (i) data segments of a first type, (ii) data segments of a second type, and (iii) data segments of a third type, wherein: a data segment of the first type comprises one or more intra-predicted blocks at the first spatial resolution; a data segment of the second type comprises at least one intra-predicted block and at least one inter-predicted block at the first spatial resolution; and a data segment of the third type comprises one or more inter-predicted blocks at the first spatial resolution.
 3. The method of claim 2, further comprising generating resized data segments (i) from the data segments of the first type using intra-mode resizing, (ii) from the data segments of the second type using mixed-mode resizing, and (iii) from the data segments of the third type using inter-mode resizing, wherein: the resized data segments have the second spatial resolution; the first data segment is a data segment of the second type; and the second data segment is a resized data segment.
 4. The method of claim 3, wherein said mixed-mode resizing comprises generating, from a data segment of the second type, a corresponding resized data segment of video data, wherein said corresponding resized data segment comprises either one or more intra-predicted blocks at the second spatial resolution or one or more inter-predicted blocks at the second spatial resolution, but not both.
 5. The method of claim 3, further comprising: removing intra-prediction coding and inter-prediction coding from the resized data segments to generate a first set of reference blocks having the second spatial resolution; storing said first set in a first buffer; subjecting said first set to feedback-loop processing to generate a corresponding second set of reference blocks having the second spatial resolution; and storing said second set in a second buffer.
 6. The method of claim 5, wherein: the first set comprises a first reference block; the second set comprises a second reference block; and the first block and the second block correspond to a same image portion at the second spatial resolution, but have different respective levels of residual errors.
 7. The method of claim 5, wherein, for each block from the first set, the second set has a corresponding block, with said two corresponding blocks being approximations of one another characterized by different respective levels of residual errors.
 8. The method of claim 5, wherein: said feedback-loop processing comprises two or more feedback-loop cycles, each comprising motion-vector refinement to reduce residual errors corresponding to the second set; and the second set is updated in the second buffer after each feedback-loop cycle.
 9. The method of claim 5, wherein said feedback-loop processing comprises a quantization operation and an inverse-quantization operation, but no discrete-cosine or integer transform and no inverse discrete-cosine or integer transform.
 10. The method of claim 5, wherein said feedback-loop processing comprises (i) a quantization operation and an inverse-quantization operation and (ii) a discrete-cosine or integer transform and an inverse discrete-cosine or integer transform.
 11. The method of claim 2, wherein the mixed-mode resizing comprises: for each data segment of the second type: determining a coding type for the data segment based on one or more reference blocks, one or more intra modes, and one or more motion vectors identified by the data segment; selecting a resizer from a bank of resizers based on one or more of (i) the determined coding type, (ii) relative geometric positions of inter- and intra-predicted blocks in an image portion represented by the data segment, (iii) an intra mode predicted for a corresponding resized data segment, and (iv) a motion-vector estimate for the corresponding resized data segment; and processing the data segment in the selected resizer to generate the corresponding resized data segment.
 12. The method of claim 2, further comprising: multiplexing the resized data segments produced by the intra-mode resizing, the mixed-mode resizing, and the inter-mode resizing to generate a second stream of partially decoded video data, said second stream of partially decoded video data having the second spatial resolution; and encoding the second stream of partially decoded video data to generate a second compressed video bit-stream, wherein the second compressed video bit-stream carries a video sequence corresponding to the first compressed video bit-stream, but at the second spatial resolution instead of the first spatial resolution.
 13. The method of claim 2, wherein: the step of partially decoding comprises a quantization operation, but no discrete-cosine or integer transform; and said mixed-mode resizing is performed in a transform domain.
 14. The method of claim 2, wherein: the step of partially decoding comprises a quantization operation and a discrete-cosine or integer transform; and said mixed-mode resizing is performed in a spatial domain.
 15. The method of claim 1, wherein the step of generating comprises: determining a coding type for the second data segment based on one or more reference blocks, one or more intra modes, and one or more motion vectors identified by the first data segment; selecting a resizer from a bank of resizers based on one or more of (i) the determined coding type, (ii) relative geometric positions of inter- and intra-predicted blocks in an image portion represented by the first data segment, (iii) an intra mode predicted for the second data segment, and (iv) a motion-vector estimate for the second data segment; and processing the first data segment in the selected resizer to generate the second data segment.
 16. The method of claim 15, wherein different resizers in the bank differ from one another by one or more of (i) a corresponding nominal range, set, or ensemble of said relative geometric positions, (ii) a corresponding nominal range, set, or ensemble of intra modes, and (iii) a corresponding nominal range, set, or ensemble of motion vectors.
 17. An apparatus, comprising: a decoding and resizing kernel configured to partially decode a first compressed video bit-stream to generate a first stream of partially decoded video data; and a mixed-mode resizer adapted to generate, from a first data segment of the first stream of partially decoded video data, a second data segment of video data, wherein: the first data segment represents an image portion at a first spatial resolution; the second data segment represents a corresponding image portion at a second spatial resolution, the second spatial resolution being different from the first spatial resolution; the first data segment comprises at least one intra-predicted block and at least one inter-predicted block at the first spatial resolution; and the second data segment comprises either one or more intra-predicted blocks at the second spatial resolution or one or more inter-predicted blocks at the second spatial resolution, but not both.
 18. The apparatus of claim 17, further comprising a demultiplexer adapted to demultiplex the partially decoded video data to generate (i) data segments of a first type, (ii) data segments of a second type, and (iii) data segments of a third type, wherein: a data segment of the first type comprises one or more intra-predicted blocks at the first spatial resolution; a data segment of the second type comprises at least one intra-predicted block and at least one inter-predicted block at the first spatial resolution; and a data segment of the third type comprises one or more inter-predicted blocks at the first spatial resolution.
 19. The apparatus of claim 17, wherein the mixed-mode resizer comprises: a coding-decision module adapted to determine a coding type for the second data segment based on one or more reference blocks, one or more intra modes, and one or more motion vectors identified by the first data segment; a bank of resizers; and controller adapted to select a resizer from the bank of resizers based on one or more of (i) the coding type determined by the coding decision module, (ii) relative geometric positions of inter- and intra-predicted blocks in an image portion represented by the first data segment, (iii) an intra mode predicted for the second data segment, and (iv) a motion-vector estimate for the second data segment, wherein the first data segment is processed in the selected resizer to generate the second data segment.
 20. The apparatus of claim 19, wherein different resizers in the bank differ from one another by one or more of (i) a corresponding nominal range, set, or ensemble of said relative geometric positions, (ii) a corresponding nominal range, set, or ensemble of intra modes, and (iii) a corresponding nominal range, set, or ensemble of motion vectors. 